The growing interest in optical networks for use in communication systems has led to growing interest in switching apparatus, such as cross-connect switches, that switch optical signals directly using micromirrors as the switching element. Generally these systems use flip-mirror chips arranged in a two-dimensional grid connected in crossbar style. An input collimated beam supplied to an input port by an optical fiber is guided along an optical path, typically either in free space or over a plane of silicon, until it is intercepted and reflected by a flip-chip micromirror that has been electronically activated to make a 45.degree. angle with the input beam, after which the beam travels in a path at a 90.degree. angle to its earlier path to an output port where it is collected by an output fiber. Such a system, for example, is described in a paper entitled "Free Space Micromachined Optical Switches with Submillisecond Switching Time for Large Scale Optical Crossconnects," IEEE Photonics Technology Letters, V10, 4, 1998, pp. 525-527.
The problem with this approach is that a small diameter collimated beam can travel only a limited distance before broadening. Accordingly unless the beam is relay-imaged by one or more intervening lenses, this problem limits the number of input and output ports feasible. Moreover placing a relay lens between each of the N.times.N flip-mirrors needed in an N.times.N switch introduces too much loss for large values of N, such as for the 1024.times.1024 switch typically required in state-of-the-art switches. Another problem is that there is considerable variation in the lengths of the various paths between the input and output ports and this complicates keeping all beams focused by interposed lenses.